Electrooculographic recordings were performed in a series of patients with malignant choroidal melanoma. The amplitudes of the light peaks were reduced in all cases compared with the recordings of the normal fellow eyes. The amount of reduction of the light peaks appeared to be dependent on localization of the tumor. The electrooculograms of eyes with tumors of the posterior pole were found to be reduced significantly. Eyes with malignant melanomas located in the peripheral fundus displayed minor reductions.